Biology 20IBiology 20IDigestive System
OR
From Food to Feces in a couple hundred steps!
DIGESTIVE SYSTEMDIGESTIVE SYSTEMHETEROTROPHIC NUTRITIONHETEROTROPHIC NUTRITION
Unable to manufacture food from inorganic molecules.
Depend on autotrophs.
AUTOTROPHIC NUTRITIONAUTOTROPHIC NUTRITION Organisms capable of synthesizing
organic molecules from simple inorganic material.
Types: photosynthesizers and chemosynthesizers.
Steps of Heterotrophic NutritionSteps of Heterotrophic Nutrition
1) Ingestion• eating or drinking• Putting organic molecules into the
system. • Heterotrophs need:
– Sugars– Amino Acids– Fatty Acids– Glycerol– Minerals– Vitamins
Steps of Heterotrophic NutritionSteps of Heterotrophic Nutrition
2) Digestion• Breakdown of macromolecules into smaller
ones that can be absorbed by the cells– Mechanical -- chewing– Chemical -- digestive enzymes
Steps of Heterotrophic NutritionSteps of Heterotrophic Nutrition
3) Absorption• Nutrients are absorbed into the blood
– Digested monomers– Water– Minerals– Vitamins
4) Egestion• Elimination of undigested material• Poop but because this is a Biology class
we will call it FECES
Steps of Heterotrophic NutritionSteps of Heterotrophic Nutrition
5) Assimilation• The conversion of nutrients into fluid or solid
parts of the organism. Assimilation can only occur after absorption has taken place.
• “You will be assimilated. Resistance is futile. ” Locutus of Borg
Digestion TermsDigestion Terms
• Mastication• To chew food
• Increases surface area for digestion
• Peristalsis • The wavelike muscular contractions of the
alimentary canal by which contents are forced onward
88
Digestion TermsDigestion Terms
• Sphincter• A ring-like muscle that normally maintains
constriction of a body passage or orifice and that relaxes as required by normal physiological functioning.
DigestionDigestion
Lipase(Pancreatic lipase)
Protease(pepsin)
Amylase (Salivary amylase)
Optimum
pHProductSubstrateSourceEnzyme
DigestionDigestion
6.1.1 - Macromolecules must be digested into their respective monomers so that our bodies can absorb them.
6.1.2 – Enzymes are needed by our body to increase the rate of digestion at our body temperature
Digestion H.2.1Digestion H.2.1
Digestive juices are secreted into the alimentary canal by glands• salivary glands
• gastric glands in the stomach wall
• pancreas
• wall of the small intestine.
Digestion H.2.2Digestion H.2.2 Exocrine glands – have secretory cells
around hollow spaces (acini) (lt. berries) which are grouped around ducts into which they secrete their products
Digestion H.2.2Digestion H.2.2
Sweat Gland Exocrine Gland
PartsParts
Organs•Mouth•Pharynx•Esophagus•Stomach•Small Intestine•Large Intestine•Anus
Glands• Salivary Glands
• Pancreas
• Liver
• Gall Bladder
Order of EventsOrder of Events
MouthMouth Hard Palate
• hard part of roof of mouth Soft Palate
• back of roof of mouth Pharynx
• chamber in throat where – nasal cavity and mouth meet
– esophagus and trachea meet
Mucus Membranes• lubricates walls of mouth for easy passage of
food
MouthMouthPurpose
• Mechanical digestion by teeth and tongue–increases surface area for action by enzymes–Mixes food thoroughly with teeth and tongue
• Chemical digestion by enzymes in salivaValue
• food easily swallowed• increases SURFACE AREA exposed for
action by digestive enzymes• thoroughly mixes the food with the TEETH
AND TONGUE
Salivary GlandsSalivary Glands•Secretions
•Saliva
•1 to 2 liters per day
•from 3 pairs of glands in the mouth
•Sub-lingual
•parotid
•Sub-mandibular
MouthMouth
Composition of Saliva
• Water
– moistens food
• Amylase (ptyalin)
– begins STARCH digestion
• Mucin
– lubricant
– binds food together for easier swallow
33 salivary glands salivary glands
• Parotid salivary gland – secrete amylase• Sublingual salivary gland – mucous
secretion that acts as a buffer and lubricant• Submandibular salivary gland – secrete
mixture of buffer, mucins and salivary amylase
• Buffers in saliva keep pH of mouth near 7.0• Prevent build up of acids produced by bacterial
action• Increase saliva when feel sick• These are exocrine glands - secretion goes
outside of body and not into the circulatory system.
MouthMouth
Control of Salivary Secretions
• Mechanical pressure
– food in the mouth
• Nervous system - glands
– Brain thinking of food in the mouth
– Signal sent to salivary glands from the brain
– Pavlov’s Dog anyone? “ring a bell and I’ll salivate”
PharynxPharynx
PharynxPharynx
Throat• Common tube through which both air and food
pass Four openings
• Nasal Cavity Mouth Cavity• Trachea Esophagus
Contains a flap of tissue called the EPIGLOTTIS to prevent food from entering the trachea
EsophagusEsophagus
Hollow muscular tube Connects pharynxpharynx to the stomachstomach
What makes the food go to the stomach? Movement of food by peristalsis
• rhythmic waves of contraction and relaxation of muscular walls
• food is squeezed through esophagus into stomach
Epiglottis and uvula shunt food into esophagus during swallowing
PeristalsisPeristalsis
PeristalsisPeristalsis
EsophagusEsophagus
Structure
• thick walled and muscular
• from pharynx to stomach
• walls contain mucus glands which
secrete mucin to lubricates food for
easy passage
StomachStomachStructurea hollow muscular pouch J shaped – shape and volume
changes from meal to meal.located high in the abdominal
cavity, just under the diaphragm where your ribs come up together – not at your waist/belt.
Structure of Stomach (con’t)Structure of Stomach (con’t) Connection between esophagus and the
stomach is regulated by cardiac sphincter.• muscular ring surround esophagus at this point• acts like a valve to open and close the tube• keeps the food from falling out of your stomach
when standing on your head. Water demo!!!! Connection between the small intestine and the
bottom end of the stomach is regulated by the pyloric sphincter.• Regulate the release of chyme into small intestine
when food is liquefied it is called chyme.
StomachStomachFUNCTIONS
• temporary storage of ingested food
• mechanical breakdown of ingested food–churning of the stomach mixes juice with food
• liquefaction of food
• beginning of protein digestion (disruption of chemical bonds in food through action of acids and enzymes)
Secretions -- Gastric JuiceSecretions -- Gastric Juice
pH plays an essential role in gastric activity• Regulated by amount of gastric
juice secretionGastric juice is secreted into
the stomach cavity by stomach cells
Secretions -- Gastric JuiceSecretions -- Gastric Juice Contains
1. Hydrochloric Acid – HCl(aq)
–pH of 1-2 –H+ and Cl- are secreted separately, becomes
HCl in stomach–Acidity:
• destroys bacteria present in food • Denatures proteins and inactivates enzymes in food• Break down plant cell walls and connective tissues
in meat• Activates Pepsin!!!!
Secretions -- Gastric JuiceSecretions -- Gastric Juice
Contains
2. Pepsin –an enzyme which begins protein
digestion
–Pepsin is produced and secreted in an inactive form called pepsinogen
• Pepsinogen convert to pepsin when pH gets to 2
Secretions -- Gastric JuiceSecretions -- Gastric Juice Why is pepsin secreted as pepsinogen, an
inactive form? Pepsin is secreted as pepsinogen first is to
protect the stomach lining.
stomach lined with a mucus coating
• prevents acid and protein digesting enzymes
from damaging wall
• Hence, stomach only digests food, and does
not have any food absorption
Digestion in StomachDigestion in Stomach pH of stomach is decreased by gastric juice When food just arrives in the stomach, pH of
stomach is still high• When pH is still above 4.5 – salivary amylase
is still active – break down carbohydrates
• When HCl in gastric juice lowers pH to 1-2, pepsin is activated – breaks down protein
– Complex proteins are broken into smaller peptide and polypeptide chain
Regulation of Gastric ActivityRegulation of Gastric Activity
1. Central Nervous System• See, smell, taste, or think of food will stimulate
increase production of gastric juice in stomach• Nervous system prepares stomach to receive
food• Production of gastric juice accelerates 500mL per
hour• Emotional states can also affect
– e.g. Anxiety – decrease stimulation & slows digestion
Regulation of Gastric ActivityRegulation of Gastric Activity
2. Hormones• Gastrin
– Produced by stomach cells– Enters blood stream– Increase secretion of HCl and Pepsinogen by
stomach cells• pH decrease
– Increase gastric motility
• When chyme enters small intestine, stomach cells secrete other hormones to temporarily inhibit gastric juice secretion
Small IntestineSmall Intestine
FUNCTION
• complete the digestion of food
– important secretions from the pancreas and
the liver.
• absorb the nutrients into the circulatory
system (blood)
Small IntestineSmall Intestine
STRUCTURE + FUNCTION About 6 meters long
• Three sections1) Duodenum
• first 25 cm • Digestion• Neutralize acids in chyme• Receives and mixes pancreatic and liver secretions
2) Jejunum • next 2 meters • Bulk of chemical digestions and nutrient absorption
3) Ileum • next 4 or 5 meters • absorption
Small IntestineSmall Intestine
STRUCTURE (con’t) the inside of the S.I. is covered with millions
of tiny finger-like projections called villi• each villus is actually covered with millions of
microvilli• the villi and microvilli increase surface area for
absorbing food molecules into blood.• 600 times more surface area
Surface of small intestine contains membrane-bound digestive enzymes
Secretions -- Pancreatic FluidSecretions -- Pancreatic Fluid
Contains1. NaHCO3 – sodium bicarbonate
– raises pH to 8 (important for enzymes to function)
2. Pancreatic Amylase – an enzyme which continues the digestion of
starch into maltose units
3. Lipase – enzyme digesting lipids into fatty acids & glycerol
Secretions -- Pancreatic FluidSecretions -- Pancreatic Fluid
4. Proteolytic Enzymes
-enzymes which continue protein digestion
-2 types:
1. protease – break down large protein complexes
2. peptidases – break down small peptide chains into individual amino acids
Example:
Trypsin (protease)– Secreted as trypsinogen in pancreas (similar to pepsinogen)– Activated into trypsin by an enzyme in membrane surface of
small intestine
Liver and Gallbladder SecretionLiver and Gallbladder Secretion
The liver produces bile– brown fluid
Bile is stored in the gallbladder when fats enter the small intestine,
the gallbladder contracts and squirts bile into the duodenum
Small IntestineSmall Intestine
• Lipase is water-soluble, only contact fat droplets on the outside surface
– Cannot break down the fat on the inside of the droplet
• bile emulsifies fats– physically prevents fats to coalesce with each
other – Fats are in smaller droplets
–greater surface area for action by lipase
• bile is NOT an enzyme because it does not cause a chemical change in fat.
Small Intestine Small Intestine H.2.9H.2.9• Explain the problem of lipid digestion in a
hydrophilic medium and the role of bile in overcoming this. –Lipid molecules tend to coalesce and are only
accessible to lipase at the lipid–water interface. Bile molecules have a hydrophilic end and a hydrophobic end, and thus prevent lipid droplets coalescing. The maximum surface is exposed to lipases. Lipase needs to be water-soluble and to have an active site to which a hydrophobic substrate binds.
Small IntestineSmall Intestine
All types of foods are acted upon.
Small Intestine H.2.5Small Intestine H.2.5 digestion of disaccharides and dipeptides is
completed by enzymes on surface membrane of intestinal villi in small intestine• sucrase
– digests sucrose
• maltase – digests maltose
• lactase – digests lactose
• aminopeptidase – breaks down dipeptides into amino acids
Small IntestineSmall Intestine
once all food molecules are at monomer stage, they are ready to be absorbed into the circulatory system through the villus on small intestine surfaces
Assignment H.3.1 Assignment H.3.1
Draw and label a Draw and label a diagram showing a diagram showing a transverse section of transverse section of the ileum as seen the ileum as seen under a light under a light microscope. Include microscope. Include mucosa and layers mucosa and layers of longitudinal and of longitudinal and circular muscle.circular muscle.
Absorption in the Small Intestine H.3.3Absorption in the Small Intestine H.3.3
Digested Nutrient
Product Method of Absorption
Site of Absorption
Small IntestineSmall Intestine
notice that glycerol recombines with 3 fatty acids to form a fat molecule which enters the lacteal instead of the capillary
Why is fat completely digested and then recombined to form a fat molecule again?
H.3.2H.3.2 Explain the structural features of an epithelial
cell of a villus as seen in electron micrographs.• Microvilli – folds of the cell membrane that increase
the surface area of the epithelial cell.• Mitochondria – provide energy for the cell to
transport nutrients.• Pinocytotic vesicles – assist with endocytosis of
nutrients.• Tight junctions – connections between epithelial
cells that maintain structure integrity of the tissue.
Large IntestineLarge Intestine
Large IntestineLarge Intestine
Material NOT absorbed by this point will enter the large intestine through another sphincter – the ilial-caecal sphincter
The caecum is a small pouch at the beginning of the large intestine.• contains a small projection called the
appendix– this is a vestigial organ which functions in
cellulose digestion in some herbivorous mammals
Functions of the Large IntestineFunctions of the Large Intestine
absorb water into blood
absorb vitamins and minerals into blood
eliminate undigested material from digestive
tract (cellulose, lignin, bile pigments, bacteria
and intestinal cells.)
Large IntestineLarge Intestine
Some bacteria live in the large
intestine of mammals
• they digest material that we are not able
to digest
a byproduct of this activity results in
the synthesis of vitamins
• Vitamin K
Rectum & AnusRectum & Anus
last section of digestive tract rectum is a holding pouch for feces feces exits the digestive tract through
a sphincter muscle called the anus. rectal veins are found near opening
• if they get inflamed…– the inside diameter of anus decreases – passage of feces is difficult and painful – called hemorrhoids or piles.
What About Fiber???What About Fiber???
fiber in the diet serves to retain water throughout the digestive
tract resulting in soft feces.
H.2.6 Outline the reasons for cellulose not being digested in
the alimentary canal. See above.
H.3.4 The materials that are not absorbed but are egested are
cellulose, lignin, bile pigments, bacteria and intestinal cells.
Biology 20Biology 20
Control of Digestive Secretions
SalivaSaliva
Nervous
• Pavlov
• Sight, smell, presence, or even thought of Sight, smell, presence, or even thought of
food stimulatesfood stimulates vagus nerve
• results in the production of saliva
Gastric JuiceGastric Juice
Nervous
• Stimulation of vagus nerve also
stimulates cells of stomach to begin
producing gastrin
Gastric JuiceGastric Juice Hormonal
• Gastrin (a hormone) is released from certain upper stomach cells into the bloodstream.
• gastrin circulates until it reaches the lower stomach cells resulting in the release of gastric juices.
• Once pH falls below 2, gastrin stops being secreted.
• If pH rises above 2.5 gastrin secretion begins again.
Pancreatic JuicePancreatic Juice Nervous
• presence ofpresence of food food in mouthin mouth and stomach stimulates pancreatic secretions
Hormonal• presence of chyme in the S.I.presence of chyme in the S.I. causes the cells of the
duodenum to secrete the hormone secretin into the blood• Secretin (a hormone) causes the pancreas to begin
producing pancreatic juice • Pancreatic Juice will enter the duodenum through the
pancreatic duct. • when acidic chyme becomes alkaline, production of
secretin stops
Liver & Gall BladderLiver & Gall Bladder
BileBile Hormonal
• presence of chyme in the S.Ipresence of chyme in the S.I. causes the cells
of the duodenum to secrete the hormone
cholesystekinin into the blood.
• This causes the gall bladder to contract,
propelling bile into the duodenum through the
bile duct
DISORDERSDISORDERS
H.2.8 Discuss the roles of gastric acid and Helicobacter pylori in the
development of stomach ulcers and stomach cancers.
•Burrows into mucus layer in stomach and produces toxins and enzymes that destroy gastric lining
•One enzyme breaks down the mucus, exposing the stomach cells to gastric juices
•Can get it from contaminated food or water. Can pass from human-to-human contact.
•Treated with combination of antibiotic and antacid.
How did they figure this out??How did they figure this out??
Barry Marshall – scientist in Australia No one would believe him that ulcers
could be due to a bacteria – the stomach is too acidic!
To prove his suspicion he drank a mixture of H. pylori himself and gave himself ulcers!
Won the Nobel prize in Medicine or Physiology, 2005 for this research
DisordersDisorders
Tapeworms are a group of parasitic worms that live in the intestinal tracts of some animals. Several different species of tapeworms can infect humans. Tapeworm disease or cestodiasis occurs most commonly after eating raw or undercooked meat or fish that contains the immature form of the tapeworm.
TapewormTapeworm
TapewormTapeworm
IntestinalDisordersIntestinalDisorders Appendicitis Cancer Celiac Disease Constipation Diarrhea Diverticulitis Hernias Inflammatory Bowel Disease Irritable Bowel Syndrome Lactose Intolerance Short Bowel Syndrome
Anorectal DisordersAnorectal Disorders
Anal Fissures Cancer Constipation Hemorrhoids Imperforate Anus
Stomach DisordersStomach Disorders
Cancer Cyclic Vomiting Syndrome Indigestion Peptic Ulcer Reflux Disease
Gallbladder DisordersGallbladder Disorders
•Gallstones
Liver DisordersLiver Disorders
Alagille Syndrome Alpha1-Antitrypsin Deficiency
Associations Cancer Children
Crigler-Najjar Syndrome Hepatic Encephalopathy Hepatitis Support Groups Transplant Wilson's Disease Zellweger Syndrome
Pancreatic DisordersPancreatic Disorders
Cancer
Cystic Fibrosis
Pancreatitis
Oral DisordersOral DisordersDrooling Dysphagia Mouth Ulcers